An Internet Protocol (IP) multimedia subsystem (IMS) is a core network subsystem added in the 3rd Generation (3G) Partnership Project (3GPP) Release 5. The IMS is based on the Session Initiation Protocol (SIP), and is an open system integrating data, voice, and IP. The IMS can satisfy a requirement of today's end users for more novel and more diversified multimedia services, and is mainly used in a 3G network, a 4th generation (4G) network, and a next generation network (NGN). As a terminal supports increasingly rich functions, a power consumption problem becomes more serious. An existing Long Term Evolution (LTE) network provides a power saving mechanism for the terminal, and allows the terminal to enter a power saving mode in a standby state. In the power saving mode, the terminal turns off a radio frequency (RF) transceiver and another communications module, and does not monitor a physical downlink control channel (PDCCH). Therefore, the terminal does not receive data or signaling. This reduces power consumption of the terminal, and prolongs a battery lifespan of the terminal.
When receiving a call request of a calling terminal for a called terminal, a network element of a core network triggers a process of paging the called terminal. If the called terminal is in a power saving mode at this moment, the called terminal cannot receive a paging request, and a call session between the calling terminal and the called terminal cannot be established. As a result, the called terminal misses a call.